1. Field of the Invention
The present invention relates to an anti-glare film that can be provided on the surface of a window or a display device. In particular, the invention relates to an anti-glare film that can be provided on the surface of a display device such as a liquid crystal display (LCD), a CRT display, an organic electroluminescent display (ELD), a plasma display (PDP), a surface emission display (SED) and a field emission display (FED) etc.
2. Description of the Related Art
In the field of display devices such as liquid crystal displays, CRT displays, EL displays and plasma displays, an anti-glare film having a concave-convex structure on the surface is known to be provided on the display surface in order to prevent the decrease in visibility caused by reflection of external light on the display surface during viewing.
For example, the following techniques are known as a manufacturing method of an anti-glare film.
A method for forming a concave-convex structure on the surface of an anti-glare film by emboss-processing.
A method of forming a concave-convex structure on the surface of an anti-glare film by coating a coating liquid in which particles are admixed to a binder matrix forming material and dispersed in the binder matrix. In the anti-glare film in which a concave-convex structure is formed on the surface by such methods, since the external light falling on the anti-glare film is scattered by the concave-convex structure of the surface so that the image of external light becomes blurred, the decrease in visibility caused by reflection of external light on the display surface can be prevented.
A variety of techniques are disclosed with respect to anti-glare films having a concave-convex structure on the surface (Patent document 1) including the following techniques, for example.
A technique using a combination of a binder matrix resin, spherical particles and irregular shape particles (Patent document 2).
A technique using a binder matrix resin and particles of a plurality of different diameters (Patent document 3).
A technique in which the cross-sectional area of concavities is specified when using an anti-glare film having surface concavities and convexities (Patent document 4).
In addition, the following techniques are also disclosed.
a technique using internal scattering together with surface scattering, setting the internal haze value (cloudiness) of the anti-glare layer to 1%-15% and setting the surface haze value (cloudiness) to 7%-30% (Patent document 5).
a technique using a binder resin and particles with a diameter of 0.5 μm to 5 μm, and setting the difference in refractive index between the binder resin and the particles to the 0.02 to 0.2 range (Patent document 6).
a technique using a binder resin and particles with a diameter of 1 μm to 5 μm, setting the difference in refractive index between the binder resin and the particles to 0.05-0.15, using an appropriate solvent, and setting the surface roughness within a predetermined range (Patent document 7).
A technique using a binder matrix resin and a plurality of types of particles and setting the difference in refractive index between the resin and the particles to 0.03-0.2 (Patent document 8).
a technique for setting the surface haze (cloudiness) to a value equal to or greater than 3 and setting the difference between a haze in the normal direction and a haze in the direction at ±60° to a value equal to or less than 4 in order to reduce a fall in contrast and a change in hue etc. when changing the angle of field of view (Patent document 9).
Anti-glare films of various configurations developed to attain a variety of objects have thus been disclosed. The performance required for anti-glare films used on the front surface of a display device differs between circumstances in which the displays are used. In other words, an optimum anti-glare film differs depending on the object of use and resolution etc. of the display device. Therefore, anti-glare films of various types corresponding to a variety of objects are needed.    <Patent document 1> JP-A-H06-018706    <Patent document 2> JP-A-2003-260748    <Patent document 3> JP-A-2004-004777    <Patent document 4> JP-A-2003-004903    <Patent document 5> JP-A-H11-305010    <Patent document 6> JP-A-H11-326608    <Patent document 7> JP-A-2000-338310    <Patent document 8> JP-A-2000-180611    <Patent document 9> JP-A-H11-160505
Anti-glare films are arranged on the surface of display devices for a note PC, a desktop PC or a TV. In recent years, display devices for TV are often watched from a distant point by users. Thus, anti-glare films are required to have not only anti-reflection properties which prevent reflection of external light falling in the display but also provide a high level of contrast and visibility to the display devices. In recent years, anti-glare films are also required to have antifouling properties such as wiping off fingerprint smears and sebum etc. which are attached or stuck to a display surface.
Anti-glare films have a concave-convex structure whereby external light is prevented from being reflected on the film surface and anti-glare properties are provided. Conventionally, anti-glare films have not been required to have a high level of antifouling properties since the smears of fingerprints etc. on the film surface were rather indistinctive due to their anti-glare properties. In anti-glare films with a high level of transparency of recent years which aims to improve contrast, however, distinct smears tend be observed on the surface of the concave-convex structure. Thus, an anti-glare film which provides both the high level of contrast and sufficient capability of wiping smears off the surface are required.
It is ordinarily possible to improve surface antifouling properties by decreasing surface free energy. In the case of an anti-glare film with a high level contrast, however, distinct and undesirable smears appear if the surface free energy is simply decreased.
If smears of fingerprints etc. are inserted to the concavities of the concave-convex structure on the surface, it becomes severely difficult to wipe the smears off the anti-glare film. In the anti-glare film with a high level of contrast, there was a problem of distinct appearance of smears inserted to the concavities and highly visible dirtiness.